Age Calculator
Calculate exact age in years, months and days from a date of birth.
About Age Calculator
Age Calculator measures the calendar difference between a date of birth and a reference date. It shows completed years, remaining months and days, alongside total days, whole weeks and the next birthday. This is useful when a form asks for age on a particular date, or when you want to compare an elapsed lifetime in calendar units.
The reference date starts as today but can be changed. Choose the relevant date rather than assuming today is correct for every task. A result such as 25 years, 2 months and 5 days describes separate calendar components; the months and days are not decimal fractions of a year. The calculation uses dates rather than a time of birth or exact elapsed hours.
How to use Age Calculator
- Choose a birth date
Use Date of birth to select the starting date.
- Choose the reference
Set Calculate age as of to today or the date relevant to your task.
- Read the calendar age
The Years, Months and Days cards update automatically when the dates are valid.
- Check the extra details
Review total days, total weeks and next birthday. Copy or Print the result if you need a record.
Example: Age on a reference date
For a date of birth of 15 June 2000 and a reference date of 20 August 2025, the calendar age is 25 years, 2 months and 5 days.
How it works
The date difference uses calendar months rather than dividing a day count by 365. It first finds the largest whole number of months that fits between the selected dates. When adding months would land beyond the last day of a shorter month, the day is clamped to that month’s end. Those whole months are separated into completed years and remaining months, and the rest of the interval is counted as days.
The extra totals describe the same interval in another way: total weeks is the whole-number week count derived from total days. The next-birthday calculation looks for the next occurrence of the birth month and day on or after the reference date. Dates are handled by the browser’s date functions; no birth time or time-zone selector is provided. The tool’s leap-day birthday convention rolls 29 February to 1 March in a non-leap year, which may differ from the convention needed for a particular form.
When is this useful?
- Check age on an application’s reference date.
- Compare a calendar age with elapsed days and weeks.
- Find the next birthday relative to a chosen date.
Things to know
- Birth date must not be later than the reference date.
- The calculator is date-based and does not measure hours or time of birth.
- Browser date handling and leap-day conventions can differ from a required form’s rules; check the specified reference and convention.
Privacy & processing
Both dates are passed to date-difference functions in this browser. The date of birth is not uploaded to a ToolMyth processing server and is not saved as an account profile.
Frequently asked questions
Can I calculate age on a date other than today?
Yes. Change Calculate age as of to the reference date you need.
Are the months a decimal part of the year?
No. They are remaining calendar months after completed years; the days are the remainder after those months.
What happens with a 29 February birthday?
Calendar differences account for month lengths. For the next-birthday result in a non-leap year, this implementation uses 1 March.
Why is the next birthday today?
The next occurrence includes the reference date itself. If that date is your birthday, the days-until value is zero.